1. Field
The present invention relates to integrated circuits and, more particularly, to high-voltage radio-frequency attenuators.
2. Background
A variable attenuator can be used in a radio-frequency receiver to attenuate large received signals before the signals reach sensitive receiver devices. A received signal from an antenna could be so large that it would damage some receiver circuits. For example, the signal from an antenna in a near-field communication (NFC) system can be as large as 100 volts.
FIG. 9 is a functional block diagram of a radio-frequency receiver illustrating use of a high-voltage radio-frequency attenuator 1011. The radio-frequency attenuator 1011 receives a radio-frequency (RF) signal from an antenna 1001 and selectively attenuates the RF signal. The attenuated RF signal is supplied to an envelope detector 1021. The envelope detector 1021 supplies its output to an analog-to-digital converter (ADC) 1031. The output of the ADC 1031 is processed by a digital signal processor 1041.
Implementing the radio-frequency receiver (e.g., for NFC) in a system-on-a-chip (SoC) integrated circuit is difficult. For example, interfacing high-voltage (e.g., 100 V differential peak-to-peak) RF signals from the antenna to receiver circuits implemented in a sub-micron SoC is challenging since the SoC fabrication technology is developed for low voltages (e.g., 1 V). Some prior NFC receivers, for example, have used capacitors and other circuit elements external to an SoC for attenuation to handle high voltages.
Additionally, the RF signals can have a large dynamic range (e.g., 55 dB). Some prior NFC receivers have used variable attenuators with significant attenuation in the lowest attenuation setting. This results in a weak signal that can degrade performance of the receiver. Accordingly, performance of the receiver can be improved if the attenuator passes the smallest RF signals with minimal attenuation.